Signal processing apparatus and method, program, and data recording medium

ABSTRACT

The present invention relates to a signal processing apparatus and method, a program, and a data recording medium configured such that the playback level of an audio signal can be easily and effectively enhanced without requiring prior analysis. An analyzer  21  generates mapping control information in the form of the root mean square of samples in a given segment of a supplied audio signal. A mapping processor  22  takes a nonlinear function determined by the mapping control information taken as a mapping function, and conducts amplitude conversion on a supplied audio signal using the mapping function. In this way, by conducting amplitude conversion of an audio signal using a nonlinear function that changes according to the characteristics in respective segments of an audio signal, the playback level of an audio signal can be easily and effectively enhanced without requiring prior analysis. The present invention may be applied to portable playback apparatus.

CROSS REFERENCE TO PRIOR APPLICATION

This application is a continuation of U.S. patent application Ser. No.13/505,443 (filed on May 1, 2012), which is a National Stage PatentApplication of PCT International Patent Application No.PCT/JP2011/070283 (filed on Sep. 6, 2011) under 35 U.S.C. §371, whichclaims priority to Japanese Patent Application No. 2010-201078 (filed onSep. 8, 2010), which are all hereby incorporated by reference in theirentirety.

TECHNICAL FIELD

The present invention relates to a signal processing apparatus andmethod, a program, and a data recording medium, and more particularly,relates to a signal processing apparatus and method, a program, and adata recording medium configured such that the playback level of anaudio signal can be easily and effectively enhanced without requiringadditional information given by prior analysis.

BACKGROUND ART

For example, in the case where movie content or music content with alarge dynamic range in audio volume is played back on a portable devicewith compact built-in speakers, not only does the audio volume becomelower overall, but audio such as low-volume dialogue in particularbecomes difficult to hear.

Thus, although normalization and automatic gain control technology doesexist as technology for making the audio of such content easier to hear,volume control becomes audibly unstable unless data is read sufficientlyfar enough ahead.

There also exists technology that boosts low-volume portions andcompresses high-volume portions of audio by means of a dynamic rangecompression process for volume. However, with a compression process, itis difficult to obtain large audio enhancement effects if generalizedvolume boost and compression settings are used. In order to obtain largeeffects, it is necessary to vary settings on a per-content basis.

For example, there exists technology that takes a sound pressure levelspecified by dialogue normalization as a basis, boosting signals with alower sound pressure level and compressing signals with a higher soundpressure level. With this technology, however, it is necessary tospecify boost and compression settings and a sound pressure level fordialogue normalization at the time of encoding the audio signal in orderto obtain sufficient effects.

Furthermore, technology has also been proposed in which, in the case ofcompressing the dynamic range of audio volume, faint sounds in an audiosignal are made easier to hear by multiplying the audio signal bycoefficients determined by the average of the absolute values of theaudio signal (see PTL 1, for example).

CITATION LIST Patent Literature

PTL 1: Japanese Unexamined Patent Application Publication No. 5-275950

SUMMARY OF INVENTION Technical Problem

Meanwhile, various types of content such as movies, music, andself-recorded content are coming to be played back on portable deviceswith compact built-in speakers. However, much of such content lacksadditional information for effective volume control given by prioranalysis done at the time of encoding, etc. as discussed above. For thisreason, there is a need for technology that effectively conducts volumecontrol even in cases where additional information obtained by prioranalysis is not included in the audio signal of given content.

Accordingly, if the technology described in PTL 1 discussed above isused, it becomes possible to suppress sudden changes in loudness whilemaking faint sounds in an audio signal easier to hear by means of acompression process, without requiring prior analysis of the audiosignal. However, the playback level of an audio signal cannot besufficiently enhanced with this technology.

For example, with the technology described in PTL 1, since amplitude issimply damped by multiplying an audio signal by a constant, there islittle freedom in amplitude conversion settings, and it cannot be saidthat the playback level of an audio signal can be effectively enhanced.Also, this technology can only be used in the case of narrowing thedynamic range of volume by amplitude conversion of an audio signal.Converting amplitude without changing the dynamic range of volume orwidening the dynamic range of volume cannot be conducted.

The present invention, being devised in light of such circumstances, isconfigured such that the playback level of an audio signal can be easilyand effectively enhanced without requiring additional information givenby prior analysis.

Solution to Problem

A signal processing apparatus of a first aspect of the present inventioncomprises analyzing means analyzing input signal characteristics,mapping processing means conducting amplitude conversion of the inputsignal on the basis of a predetermined linear function or nonlinearfunction, weighting controlling means respectively multiplying aplurality of the input signals, which have been respectivelyamplitude-converted on the basis of mutually different functions by aplurality of the mapping processing means, by weights determined by theanalysis result for the input signal characteristics, and adding meansgenerating an output signal by adding together the plurality of inputsignals which have been multiplied by the weights.

The analyzing means may be made to compute a value expressing theaverage sample value of samples included in a given segment of the inputsignal as the analysis result.

The analysis result may be taken to be the root mean square or a movingaverage of sample values of samples included in the given segment.

In the case where amplitude conversion is conducted on the input signalfor each of a plurality of channels to generate an output signal foreach channel, the analyzing means may be made to compute one analysisresult shared by all channels.

It may be configured such that the weights are determined by theanalysis result for every single sample of the input signal.

It may be configured such that the weights are determined by theanalysis result for every given number of two or more consecutivesamples of the input signal.

A signal processing method or program of a first aspect of the presentinvention includes the steps of analyzing input signal characteristics,conducting amplitude conversion of the input signal on the basis of apredetermined linear function or nonlinear function, respectivelymultiplying a plurality of the input signals, which have beenamplitude-converted on the basis of a plurality of mutually differentfunctions, by weights determined by the analysis result for the inputsignal characteristics, and generating an output signal by addingtogether the plurality of input signals which have been multiplied bythe weights.

In a first aspect of the present invention, input signal characteristicsare analyzed, amplitude conversion of the input signal is conducted onthe basis of a predetermined linear function or nonlinear function, aplurality of the input signals, which have been respectivelyamplitude-converted on the basis of mutually different functions by aplurality of the mapping processing means, are respectively multipliedby weights determined by the analysis result for the input signalcharacteristics, and an output signal is generated by adding togetherthe plurality of input signals which have been multiplied by theweights.

A data recording medium of a second aspect of the present invention hasrecorded thereon an output signal obtained by analyzing input signalcharacteristics, conducting amplitude conversion of the input signal onthe basis of a predetermined linear function or nonlinear function,respectively multiplying a plurality of the input signals, which havebeen amplitude-converted on the basis of a plurality of mutuallydifferent functions, by weights determined by the analysis result forthe input signal characteristics, and adding together the plurality ofinput signals which have been multiplied by the weights.

A signal processing apparatus of a third aspect of the present inventioncomprises analyzing means analyzing input signal characteristics, andmapping processing means generating an output signal by conductingamplitude conversion of the input signal on the basis of a nonlinearfunction determined by the analysis result for the input signalcharacteristics.

The analyzing means may be made to compute a value expressing theaverage sample value of samples included in a given segment of the inputsignal as the analysis result.

The analysis result may be taken to be the root mean square or a movingaverage of sample values of samples included in the given segment.

In the case where amplitude conversion is conducted on the input signalfor each of a plurality of channels to generate an output signal foreach channel, the analyzing means may be made to compute one analysisresult shared by all channels on the basis of the input signals in theplurality of channels.

The nonlinear function may be determined by the analysis result forevery single sample of the input signal.

The nonlinear function may be determined by the analysis result forevery given number of two or more consecutive samples of the inputsignal.

A signal processing method or program of a third aspect of the presentinvention includes the steps of analyzing input signal characteristics,and generating an output signal by conducting amplitude conversion ofthe input signal on the basis of a nonlinear function determined by theanalysis result for the input signal characteristics.

In a third aspect of the present invention, input signal characteristicsare analyzed, and an output signal is generated by conducting amplitudeconversion of the input signal on the basis of a nonlinear functiondetermined by the analysis result for the input signal characteristics.

A data recording medium of a fourth aspect of the present invention hasrecorded thereon an output signal obtained by analyzing input signalcharacteristics, and conducting amplitude conversion of the input signalon the basis of a nonlinear function determined by the analysis resultfor the input signal characteristics.

Advantageous Effects of Invention

According to the first through fourth aspects of the present invention,the playback level of an audio signal can be easily and effectivelyenhanced without requiring additional information given by prioranalysis.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a diagram illustrating an exemplary configuration of a firstembodiment of an audio signal processing apparatus applying the presentinvention.

FIG. 2 is a flowchart explaining a conversion process.

FIG. 3 is a diagram illustrating exemplary mapping functions.

FIG. 4 is a diagram illustrating exemplary mapping functions.

FIG. 5 is a diagram illustrating exemplary mapping functions.

FIG. 6 is a diagram illustrating another exemplary configuration of anaudio signal processing apparatus.

FIG. 7 is a flowchart explaining a conversion process.

FIG. 8 is a diagram illustrating another exemplary configuration of anaudio signal processing apparatus.

FIG. 9 is a flowchart explaining a conversion process.

FIG. 10 is a diagram illustrating exemplary mapping functions.

FIG. 11 is a diagram illustrating another exemplary configuration of anaudio signal processing apparatus.

FIG. 12 is a flowchart explaining a conversion process.

FIG. 13 is a block diagram illustrating an exemplary configuration of acomputer.

DESCRIPTION OF EMBODIMENTS

Hereinafter, embodiments applying the present invention will bedescribed with reference to the drawings.

First Embodiment Configuration of Audio Signal Processing Apparatus

FIG. 1 is a diagram illustrating an exemplary configuration of anembodiment of an audio signal processing apparatus applying the presentinvention.

The audio signal processing apparatus 11 is provided in a portableplayback apparatus that plays back content consisting of video signalsand audio signals, for example, and conducts amplitude conversion on aninput audio signal such that the playback level is enhanced, and outputsthe amplitude-converted audio signal. Note that hereinafter, an audiosignal input specifically input into the audio signal processingapparatus 11 is designated an input signal, while an audio signalobtained by amplitude-converting an input signal is designated an outputsignal.

The audio signal processing apparatus 11 is composed of an analyzer 21,a mapping processor 22, an output unit 23, and a drive 24.

The analyzer 21 analyzes the characteristics of a supplied input signal,and supplies mapping control information indicating the analysis resultsto the mapping processor 22.

The mapping processor 22 uses mapping control information supplied fromthe analyzer 21 to conduct a mapping process on a supplied input signaland enhance the playback level of the input signal. In the mappingprocess, linear or non-linear amplitude conversion is conducted on aninput signal. The mapping processor 22 supplies the output unit 23 withan output signal obtained by the mapping process.

The output unit 23 may output an output signal supplied from the mappingprocessor 22 to a subsequent audio output unit, etc. or supply it to thedrive 24. The drive 24 records an output signal supplied from the outputunit 23 to a removable medium 25, which is a recording medium able to befreely inserted into and removed from the drive 24.

[Description of Conversion Process]

Next, operation of the audio signal processing apparatus 11 in FIG. 1will be described.

The audio signal processing apparatus 11 conducts a conversion processupon being supplied with an input signal, and generates and outputs anoutput signal. Hereinafter, a conversion process conducted by the audiosignal processing apparatus 11 will be described with reference to theflowchart in FIG. 2.

In step S11, the analyzer 21 analyzes the characteristics of a suppliedinput signal, and generates mapping control information.

Specifically, the analyzer 21 may, for example, perform the computationin the following Eq. 1, and compute the root mean square RMS(n) for thenth sample of the input signal as mapping control information for thenth sample.

$\begin{matrix}{\lbrack {{Expression}\mspace{14mu} 1} \rbrack\mspace{596mu}} & \; \\{{{RMS}(n)} = {20.0 \times {\log_{10}( \sqrt{\frac{1}{N} \cdot {\sum\limits_{m = {n - {N/2}}}^{m + {N/2} - 1}\;( {x(m)} )^{2}}} )}}} & (1)\end{matrix}$

In Eq. 1 herein, x(m) represents the sample value of the mth sample ofthe input signal (the input signal value). Also, in Eq. 1, the inputsignal values, or in other words the sample values of each input signalsample, are taken to be normalized such that −1≦x(m)≦1.

Consequently, the root mean square RMS(n) is obtained by taking thelogarithm of the square root of the mean square value of the samplevalues for samples included in a segment consisting of N consecutivesamples centered about the nth sample, and multiplying the value thusobtained by the constant 20.

Values of the root mean square RMS(n) obtained in this way decrease withdecreasing absolute values of the sample values for the samples in aspecific segment centered about the nth sample of the input signal beingprocessed. In other words, the root mean square RMS(n) decreases as theoverall audio volume decreases in a specific segment that includes theinput signal sample being processed.

Once the analyzer 21 analyzes an input signal and mapping controlinformation is obtained, the mapping control information is supplied tothe mapping processor 22.

In step S12, the mapping processor 22 uses mapping control informationfrom the analyzer 21 to conduct a mapping process on a supplied inputsignal, and generates an output signal.

Specifically, the mapping processor 22 converts amplitude bysubstituting the sample value x of the nth sample of an input signalwith the nonlinear mapping function f(x) expressed in the following Eq.2. In other words, the value obtained by substituting the sample value xwith the mapping function f(x) is taken to be the sample value of thenth sample of the output signal.

$\begin{matrix}{\lbrack {{Expression}\mspace{14mu} 2} \rbrack\mspace{596mu}} & \; \\{{f(x)} = \{ \begin{matrix}{{( {2 - \alpha} )x} - ( {\alpha - 1} )} & ( {{- 1.0} \leq x < {- 0.5}} ) \\{\alpha\; x} & ( {{- 0.5} \leq x \leq 0.5} ) \\{{( {2 - \alpha} )x} + ( {\alpha - 1} )} & ( {0.5 < x \leq 1.0} )\end{matrix} } & (2)\end{matrix}$

In Eq. 2 herein, the sample value x of an input signal is taken to benormalized to a value from −1 to 1. Also, in Eq. 2, α represents acontrol factor, with the control factor α being a numerical valuedetermined by the value of the mapping control information.

According to Eq. 2, in the case where the sample value x is −1 orgreater but less than −0.5, the mapping function f(x) becomes(2−α)x−(α−1), whereas in the case where the sample value x is between−0.5 and 0.5 inclusive, the mapping function f(x) becomes αx. Also, inthe case where the sample value x is greater than 0.5 but 1 or less, themapping function f(x) becomes (2−α)x+(α−1).

Additionally, the control factor α is taken to be a value determined bythe following Eq. 3, for example.

$\begin{matrix}{\lbrack {{Expression}\mspace{14mu} 3} \rbrack\mspace{596mu}} & \; \\{\alpha = \{ \begin{matrix}{\frac{{RMS}(n)}{- 30.0} + 1.0} & ( {{- 30.0} < {{RMS}(n)} \leq 0.0} ) \\2.0 & ( {{{RMS}(n)} \leq {- 30.0}} )\end{matrix} } & (3)\end{matrix}$

In other words, in the case where the value of the root mean squareRMS(n) given to be the mapping control information is greater than −30but 0 or less, the value of the control factor α is taken to be(RMS(n)/−30)+1. At this point, the range of values that the controlfactor α may take becomes 1≦α<2, with the value of the control factor αdecreasing as the root mean square RMS(n) increases. Also, in the casewhere the value of the root mean square RMS(n) is −30 or less, the valueof the control factor α is taken to be 2.

Consequently, the control factor α increases as the volume of audiobased on an input signal decreases overall, or in other words as theroot mean square RMS(n) decreases. As a result, the slope of the mappingfunction f(x) increases as illustrated in FIG. 3.

In FIG. 3 herein, the horizontal axis represents the sample value x ofan input signal, while the vertical axis represents the value of themapping function f(x). Also, the line f11, the curve f12, and the curvef13 represent the mapping function f(x) for a control factor α of 1.0,1.4, and 1.8, respectively.

As FIG. 3 demonstrates, as the volume of audio based on an input signaldecreases overall, amplitude conversion of the input signal is conductedusing a steeper mapping function f(x). In other words, as the audiovolume decreases overall, the rate of change in f(x) versus change inthe sample value x increases in the mapping function f(x).

For example, for a control factor α of 1.0 and a mapping function f(x)expressed by the line f11, a sample value in the input signal is takenwithout change as a sample value in the output signal. In contrast, witha control factor α of 1.8 and a mapping function f(x) expressed by thecurve f13, the slope of the mapping function becomes greater than theslope of the mapping function expressed by the line f11 in the segmentwhere the sample value x of an input signal is between −0.5 and 0.5inclusive.

In this way, as the volume of audio in an input signal decreasesoverall, amplitude conversion of the input signal is conducted using amapping function f(x) with steeper characteristics in the segment formost sample values x, including sample values x equal to 0.

Consequently, in segments where the audio of an input signal is at lowvolume overall, the input signal is amplitude-converted such thatlow-volume audio is converted into higher-volume audio, enhancing theplayback level of the input signal. Thus, even faint sounds that havebeen conventionally difficult to hear can be made easier to hear by amapping process conducted on an input signal, even in cases where moviesor other content with a large dynamic range in volume is played back ona portable device housing compact speakers.

Also, even in segments where the audio of an input signal is at highvolume overall, amplitude conversion of the input signal is conductedusing a mapping function f(x) with appropriately steep characteristicson the parts of the signal with small sample values x therein.

Consequently, even in segments where the audio of an input signal is athigh volume overall, the input signal is amplitude-converted such thatfaint audio therein is converted into loud audio, enhancing the playbacklevel of the input signal. Thus, even sounds that conventionally havebeen played back comparatively loudly become heard even more loudly.

Moreover, with the audio signal processing apparatus, 11, it is notnecessary to analyze an input signal in advance and add additionalinformation for amplitude conversion to the input signal, or to readahead long segments of an input signal and analyze the read input signalbefore conducting amplitude conversion.

Also, by varying a nonlinear mapping function f(x) according to acontrol factor α, amplitude conversion with a higher degree of freedomcan be realized. In other words, by taking the nonlinear function withthe most effective characteristics as the mapping function depending onthe overall characteristics of a specific segment of an input signal,amplitude conversion can be conducted while taking into account not onlythe characteristics of the segment containing the sample beingprocessed, but also the magnitude of the sample value for that sample.

For example, with the technology described in PTL 1 discussed earlier,an audio signal is multiplied by a constant determined by the average ofthe absolute values of the audio signal, irrespectively of the audiosignal values. In other words, a sample of an audio signal would bealways a constant multiple, regardless of the magnitude of the amplitudeof that sample.

For this reason, if a computation method that multiplies an audio signalby a constant is determined with respect to comparatively low-volumeaudio in order to increase the volume of that audio, high-volume audiomay not reach a suitable volume even if the audio signal is multipliedby a constant.

In contrast, with the audio signal processing apparatus 11, if themapping function is taken to be a nonlinear function, amplitudeconversion with a high degree of freedom becomes possible, such asgreatly increasing the amplitude in the case where the sample amplitude(sample value) is small, but not greatly changing the amplitude in thecase where the sample amplitude is large. Thus, the playback level of anaudio signal can be effectively enhanced, such as by convertinglow-volume audio into higher-volume audio while also not significantlychanging the volume of audio that was at high volume to begin with.

Furthermore, by appropriately setting a mapping function f(x), thedynamic range in audio volume can be widened, kept the same, or thedynamic range can be narrowed by amplitude conversion.

In this way, with the audio signal processing apparatus 11, the playbacklevel of an audio signal can be easily and effectively enhanced.

Returning to the description of the flowchart in FIG. 2, upon generatingan output signal by means of a mapping process, the mapping processor 22supplies the obtained output signal to the output unit 23.

In step S13, the output unit 23 outputs an output signal supplied fromthe mapping processor 22 to a subsequent unit, and the conversionprocess ends. The output unit 23 may also supply the output signal tothe drive 24 as necessary, with the drive 24 recording the suppliedoutput signal to the removable medium 25.

As above, the audio signal processing apparatus 11 analyzes thecharacteristics of an input signal and uses a mapping function thatvaries according to the analysis results to conduct a mapping process onthe input signal and generate an output signal.

The root mean square RMS(n) taken as the mapping control informationobtained by analyzing an input signal expresses the average magnitude ofsample values in a given segment of an input signal, or in other words,an amplitude distribution of samples in a given segment. For example, inthe case where the root mean square RMS(n) is small, many samples of lowamplitude are contained in the input signal, whereas in the oppositecase where the root mean square RMS(n) is large, many samples of highamplitude are contained in the input signal.

In the audio signal processing apparatus 11, by using the root meansquare RMS(n) to generate a mapping function with more effectivecharacteristics and then conduct a mapping process, an input signal canbe easily converted into an output signal having an ideal amplitudedistribution.

<Modification 1>

Although the foregoing describes using a function which is linear ineach segment as the mapping function, a function with smoother curvesmay also be used as the mapping function. In such cases, the nonlinearfunction expressed in the following Eq. 4 may be taken to be the mappingfunction, for example.

$\begin{matrix}{\lbrack {{Expression}\mspace{14mu} 4} \rbrack\mspace{596mu}} & \; \\{{f(x)} = {\frac{2}{1 + {\mathbb{e}}^{{- \alpha}\; x}} - {1\mspace{59mu}( {{- 1.0} \leq x \leq 1.0} )}}} & (4)\end{matrix}$

In Eq. 4 herein, x represents the sample value of an input signalsample. The input signal sample value x is taken to be normalized to avalue from −1 to 1. Also, the control factor α in Eq. 4 is determined bythe following Eq. 5.

$\begin{matrix}{\lbrack {{Expression}\mspace{14mu} 5} \rbrack\mspace{596mu}} & \; \\{\alpha = \{ \begin{matrix}{{\frac{{RMS}(n)}{- 30.0} \times 5.0} + 1.0} & ( {{- 30.0} < {{RMS}(n)} \leq 0.0} ) \\10.0 & ( {{{RMS}(n)} \leq {- 30.0}} )\end{matrix} } & (5)\end{matrix}$

In other words, in the case where the value of the root mean squareRMS(n) given to be the mapping control information is greater than −30but 0 or less, the value of the control factor α is taken to be(RMS(n)/−30)×5+5. At this point, the range of values that the controlfactor α may take becomes 5≦α<10, with the value of the control factor αdecreasing as the root mean square RMS(n) increases. Also, in the casewhere the value of the root mean square RMS(n) is −30 or less, the valueof the control factor α is taken to be 10.

Consequently, the control factor α increases as the volume of audiobased on an input signal decreases overall, or in other words as theroot mean square RMS(n) decreases. As a result, the slope of the mappingfunction f(x) varies as illustrated in FIG. 4.

In FIG. 4 herein, the horizontal axis represents the sample value x ofan input signal, while the vertical axis represents the value of themapping function f(x). Also, the curves f21 to f23 represent the mappingfunction f(x) for a control factor α of 5, 7, and 10, respectively.

As FIG. 4 demonstrates, as the volume of audio based on an input signaldecreases overall, amplitude conversion of the input signal is conductedusing a mapping function f(x) with a greater overall rate of changeversus change in the sample value x. In other words, as the volume ofaudio based on an input signal decreases overall, a steeper mappingfunction f(x) is used in the segment for most sample values x, includingsample values x equal to 0.

In this way, in the case of using the mapping function expressed in Eq.4 and the control factor α expressed in Eq. 5, the mapping functiontakes on steeper characteristics as the root mean square RMS(n)decreases, similarly to the case of using the mapping function in Eq. 2and the control factor α in Eq. 3. Likewise in this case, the playbacklevel of an audio signal can be more easily and effectively enhancedwithout requiring prior analysis or reading ahead of the input signal.Furthermore, faint sounds that have been conventionally difficult tohear can be made easier to hear, while in addition, even sounds thathave been comparatively loud conventionally become even easier to hear.

<Modification 2>

Meanwhile, since the mapping function in Eq. 4 discussed above is anexponential function, if computation of the mapping process is performedby a computer or DSP (Digital Signal Processor), etc., the computationalload typically increases. Thus, by adopting the cubic function expressedin the following Eq. 6 as the mapping function, for example, thecomputational load can be decreased, and the mapping process can beconducted more rapidly.

$\begin{matrix}{\lbrack {{Expression}\mspace{14mu} 6} \rbrack\mspace{596mu}} & \; \\{{f(x)} = {\frac{\alpha}{\alpha - 1}( {x - {\frac{1}{\alpha}x^{3}}} )\mspace{59mu}( {{- 1.0} \leq x \leq 1.0} )}} & (6)\end{matrix}$

In Eq. 6 herein, x represents the sample value of an input signalsample. The input signal sample value x is taken to be normalized to avalue from −1 to 1. Also, the control factor α in Eq. 6 is determined bythe following Eq. 7.

$\begin{matrix}{\lbrack {{Expression}\mspace{14mu} 7} \rbrack\mspace{596mu}} & \; \\{\alpha = \{ \begin{matrix}100.0 & ( {{- 0.9} \leq {{RMS}(n)} \leq 0.0} ) \\{\frac{- 30.0}{{RMS}(n)} \times 3.0} & ( {{- 30.0} < {{RMS}(n)} < {- 0.9}} ) \\3.0 & ( {{{RMS}(n)} \leq {- 30.0}} )\end{matrix} } & (7)\end{matrix}$

In other words, in the case where the value of the root mean squareRMS(n) given to be the mapping control information is between −0.9 and 0inclusive, the control factor α is taken to be 100, whereas in the casewhere the value of the root mean square RMS(n) is greater than −30 butless than −0.9, the value of the control factor α is taken to be−30/RMS(n)×3. At this point, the range of values that the control factorα may take becomes 3<α<100, with the value of the control factor αincreasing as the root mean square RMS(n) increases. Also, in the casewhere the value of the root mean square RMS(n) is −30 or less, the valueof the control factor α is taken to be 3.0.

Consequently, the control factor α decreases as the volume of audiobased on an input signal decreases overall, or in other words as theroot mean square RMS(n) decreases. As a result, the mapping functionf(x) varies steeply as illustrated in FIG. 5.

In FIG. 5 herein, the horizontal axis represents the sample value x ofan input signal, while the vertical axis represents the value of themapping function f(x). Also, the curves f31 to f33 represent the mappingfunction f(x) for a control factor α of 100, 5, and 3, respectively.

As FIG. 5 demonstrates, as the volume of audio based on an input signaldecreases overall, amplitude conversion of the input signal is conductedusing a mapping function f(x) with a greater overall rate of changeversus change in the sample value x.

In this way, in the case of using the mapping function expressed in Eq.6 and the control factor α expressed in Eq. 7, the mapping functiontakes on steeper characteristics as the root mean square RMS(n)decreases, similarly to the case of using the mapping function in Eq. 2and the control factor α in Eq. 3. Likewise in this case, the playbacklevel of an audio signal can be more easily and effectively enhancedwithout requiring prior analysis or reading ahead of the input signal.Furthermore, faint sounds that have been conventionally difficult tohear can be made easier to hear, while in addition, even sounds thathave been comparatively loud conventionally become even easier to hear.

Note that the mapping function f(x) may be any function insofar as thefunction becomes −1≦f(x)≦1 for sample values x where −1≦x≦1.

Also, although an example of using the root mean square RMS(n) asmapping control information for determining a control factor α isdescribed in the foregoing, the mapping control information may beanother element, or may be taken to be mapping control informationcombining multiple elements. For example, the moving average of samplevalues for samples in a given segment of an input signal, the number ofzero-crossings in samples in a given segment, or a value expressing thetonality of an input signal may also be taken to be mapping controlinformation. In other words, it may be configured such that elementswith large processing effects, whereby audio suitable for listening isobtained by the mapping process, may be used for the mapping function,the control factor α, and the mapping control information.

Also, although the foregoing describes conducting a mapping process bycomputing mapping control information and a control factor α for themapping function for every single sample of an input signal, the mappingprocess may also be conducted by computing mapping control informationand a control factor α for every two or more consecutive samples. Forexample, in such cases, the mapping control information and controlfactor computed for one sample may be successively used for a givennumber of consecutive samples.

Furthermore, it may also be configured such that the method forcomputing mapping control information or a control factor is variedaccording to the output device for the output signal, etc., so as toadjust the degree of enhancement to the playback level of an audiosignal. Specifically, the relationship between the control factor α andthe mapping control information may be varied, such as by usingdifferent formulas for computing the control factor α, for example.

Second Embodiment Configuration of Audio Signal Processing Apparatus

Meanwhile, in the case where an audio signal given as an input signalhas two or more channels, inter-channel volume balance of audio based onthe output signal may change if analysis of input signal characteristicsor a mapping process is conducted independently on each channel.

For this reason, it is desirable to conduct identical analyses andmapping processes on the input signals in all channels. Thus, it mayalso be configured such that characteristics are analyzed for the inputsignals in all channels, and a mapping process is conducted using oneset of mapping control information obtained from the analysis results.In such cases, the audio signal processing apparatus may be configuredas illustrated in FIG. 6, for example.

The audio signal processing apparatus 51 is composed of an analyzer 21,a mapping processor 22, a mapping processor 61, an output unit 23, and adrive 24. In FIG. 6 herein, like numerals are given to portionscorresponding to the case in FIG. 1, and description of such portionswill be reduced or omitted.

Input signals are supplied to the audio signal processing apparatus 51as a left-channel audio signal and a right-channel audio signalconstituting a movie or other content, for example. In other words, theleft-channel input signal is supplied to the analyzer 21 and the mappingprocessor 22, while the right-channel input signal is supplied to theanalyzer 21 and the mapping processor 61.

The analyzer 21 analyzes the respective characteristics of the suppliedleft- and right-channel input signals, generates mapping controlinformation on the basis of the two sets of analysis results thusobtained, and supplies the mapping control information to the mappingprocessor 22 and the mapping processor 61.

The mapping processor 61 uses the mapping control information suppliedfrom the analyzer 21 to conduct a mapping process on the suppliedright-channel input signal and generates a right-channel output signal.At this point, a process similar to that of the mapping processor 22 isconducted in the mapping processor 61. The mapping processor 61 suppliesthe right-channel output signal obtained by the mapping process to theoutput unit 23.

In this way, in the audio signal processing apparatus 51, shared mappingcontrol information is used to conduct mapping processes in the mappingprocessor 22 and the mapping processor 61.

The output unit 23 may output the left- and right-channel output signalssupplied from the mapping processor 22 and the mapping processor 61 to asubsequent unit or to the drive 24 for recording to the removable medium25.

[Description of Conversion Process]

Next, a conversion process conducted by the audio signal processingapparatus 51 will be described with reference to the flowchart in FIG.7.

In step S41, the analyzer 21 analyzes the characteristics of suppliedleft- and right-channel input signals. For example, the analyzer 21 mayperform the computation in Eq. 1 discussed earlier, and compute aleft-channel root mean square RMS(n) and a right-channel root meansquare RMS(n).

In step S42, the analyzer 21 generates mapping control information onthe basis of the input signal characteristics analysis results, andsupplies the mapping control information to the mapping processor 22 andthe mapping processor 61. For example, the analyzer 21 may compute theaverage of the left-channel root mean square RMS(n) and theright-channel root mean square RMS(n), and take the obtained average tobe the mapping control information.

However, it may also be configured such that the larger value of theleft-channel root mean square RMS(n) and the right-channel root meansquare RMS(n) may be taken without change as the mapping controlinformation. Also, samples from the left-channel input signal andsamples from the right-channel input signal may be used to compute asingle root mean square RMS(n), etc. as the mapping control information.

Once the operation in step S42 is conducted and mapping controlinformation is generated, the operations in steps S43 and S44 aresubsequently conducted and the conversion process ends. However, sincethese processing operations are similar to the operations in steps S12and S13 of FIG. 2, their description will be reduced or omitted.

However, in step S43, the mapping control information is used in themapping processor 22 and the mapping processor 61, and a left-channeloutput signal and a right-channel output signal are respectivelygenerated with identical mapping functions and control factors.

In so doing, the audio signal processing apparatus 51 analyzes thecharacteristics of left- and right-channel input signals, generatescommon mapping control information for the left and right channels, anduses the obtained mapping control information to conduct an identicalmapping process on each channel. By using common mapping controlinformation for the left and right channels to conduct an identicalmapping process on per-channel input signals in this way, the playbacklevel of an audio signal can be enhanced without changing theinter-channel volume balance.

Although the foregoing describes a case where two left- andright-channel input signals are input, an input signal may also becomposed of three or more channels. Even in such cases, common mappingcontrol information is generated for all channels.

Third Embodiment Configuration of Audio Signal Processing Apparatus

Also, although the foregoing describes using a single mapping functionto generating an output signal, a plurality of linear or nonlinearmapping functions may be prepared, and it may be configured such that anoutput signal is generated by selectively using those mapping functionsaccording to the mapping control information. In such cases, changes inthe output that occur due to switching the mapping function used togenerate the output signal can be made smoother by taking the outputsignal to be a weighted sum of outputs from plural mapping functionsdepending on the mapping control information.

In this way, in the case of generating an output signal by using aplurality of mapping functions, an audio signal processing apparatus maytake the configuration illustrated in FIG. 8, for example.

Namely, the audio signal processing apparatus 91 is composed of ananalyzer 21, mapping processors 101-1 to 101-M, a weighting controller102, an adder 103, an output unit 23, and a drive 24. In FIG. 8 herein,like numerals are given to portions corresponding to the case in FIG. 1,and description of such portions will be reduced or omitted.

The mapping processors 101-1 to 101-M each conduct a mapping process ona supplied input signal using respectively different mapping functions,and supply the output signals obtained as a result to the weightingcontroller 102. Note that hereinafter, the mapping processors 101-1 to101-M will also be simply designated the mapping processors 101 in caseswhere it is not necessary to individually distinguish them.

The weighting controller 102 multiplies output signals supplied from themapping processors 101 by distribution ratios, which are weightsdetermined by mapping control information supplied from the analyzer 21,and supplies the result to the adder 103. In other words, the weightingcontroller 102 is provided with multipliers 111-1 to 111-M. Themultipliers 111-1 to 111-M multiply output signals supplied from themapping processors 101-1 to 101-M by distribution ratios α₁ to α_(M)determined by mapping control information, and supply the results to theadder 103.

Note that hereinafter, the multipliers 111-1 to 111-M will also besimply designated the multipliers 111 in cases where it is not necessaryto individually distinguish them.

The adder 103 adds together M output signals supplied from themultipliers 111, and supplies the final output signal obtained as aresult to the output unit 23.

[Description of Conversion Process]

Next, a conversion process conducted by the audio signal processingapparatus 91 will be described with reference to the flowchart in FIG.9.

In step S71, the analyzer 21 analyzes the characteristics of a suppliedinput signal. For example, the analyzer 21 may perform the computationin Eq. 1 discussed earlier, compute the root mean square RMS(n) for thenth sample of the input signal as mapping control information, andsupply the mapping control information to the weighting controller 102.

In step S72, the mapping processors 101 conduct a mapping process onsupplied input signals, and supply the obtained output signals to themultipliers 111.

For example, assume that the audio signal processing apparatus 91 isprovided with four mapping processors 101-1 to 101-4. In this case, themapping processors 101-1 to 101-4 conduct a mapping process on suppliedinput signals by using the mapping functions f₁(x) to f₄(x) expressed inthe following Eqs. 8 to 11. In other words, the value obtained bysubstituting in a mapping function for the sample value x of the nthsample of an input signal is taken to be the sample value of the nthsample of an output signal.

$\begin{matrix}{\lbrack {{Expression}\mspace{14mu} 8} \rbrack\mspace{580mu}} & \; \\{{f_{1}(x)} = {x\mspace{34mu}( {{- 1.0} \leq x \leq 1.0} )}} & (8) \\{{f_{2}(x)} = {\frac{2}{1 + {\mathbb{e}}^{{- 5}\; x}} - {1\mspace{31mu}( {{- 1.0} \leq x \leq 1.0} )}}} & (9) \\{{f_{3}(x)} = {\frac{2}{1 + {\mathbb{e}}^{{- 7}\; x}} - {1\mspace{31mu}( {{- 1.0} \leq x \leq 1.0} )}}} & (10) \\{{f_{4}(x)} = {\frac{2}{1 + {\mathbb{e}}^{{- 10}\; x}} - {1\mspace{31mu}( {{- 1.0} \leq x \leq 1.0} )}}} & (11)\end{matrix}$

In Eqs. 8 to 11 herein, x represents the sample value of an input signalsample. In Eqs. 8 to 11, the input signal sample value x is taken to benormalized to a value from −1 to 1.

These mapping functions f₁(x) to f₄(x) are functions ordered from themapping function f₄(x) to the mapping function f₁(x) in order ofsteepest characteristics.

In FIG. 10 herein, the mapping functions f₁(x) to f₄(x) are illustratedin the upper-left, the upper-right, the lower-left, and the lower-right,respectively. Also, in FIG. 10, the horizontal axis represents thesample value x of an input signal, while the vertical axis representsthe value of a mapping function.

For example, in the drawing, the mapping function f₁(x)=x illustrated inthe upper-left is a linear first-order function, in which a sample valuex in an input signal is taken without change as a sample value in anoutput signal. Also, the mapping functions f₂(x) to f₄(x) are nonlinearexponential functions ordered from the mapping function f₄(x) to themapping function f₂(x) in order of steepest characteristics in thesegment for most sample values x, including sample values x equal to 0.In other words, the mapping functions are ordered from the mappingfunction f₄(x) to the mapping function f₂(x) in order of the highestrate of change in the mapping function output versus change in thesample value x.

Returning to description of the flowchart in FIG. 9, in step S73, theweighting controller 102 multiplies output signals supplied from themapping processors 101 by distribution ratios acting as weights, on thebasis of mapping control information supplied from the analyzer 21.

For example, assume that the audio signal processing apparatus 91 isprovided with four mapping processors 101-1 to 101-4. In this case, theweighting controller 102 performs the computation expressed in thefollowing Eq. 12 and computes distribution ratios α₁ to α₄ for themapping functions f₁(x) to f₄(x), on the basis of the root mean squareRMS(n) given as mapping control information.

$\begin{matrix}{\lbrack {{Expression}\mspace{14mu} 9} \rbrack\mspace{580mu}} & \; \\\{ \begin{matrix}\begin{matrix}{{\alpha_{1} = {1.0 - \frac{{RMS}(n)}{- 12.0}}},{\alpha_{2} = {1.0 - \alpha_{1}}},} \\{\alpha_{3} = {\alpha_{4} = 0.0}}\end{matrix} & ( {{- 12.0} < {{RMS}(n)} \leq 0.0} ) \\\begin{matrix}{{\alpha_{1} = 0.0},{\alpha_{2} = {1.0 - \frac{{{RMS}(n)} + 12.0}{- 12.0}}},} \\{{\alpha_{3} = {1.0 - \alpha_{2}}},{\alpha_{4} = 0.0}}\end{matrix} & ( {{- 24.0} < {{RMS}(n)} \leq {- 12.0}} ) \\\begin{matrix}{{\alpha_{1} = {\alpha_{2} = 0.0}},} \\{{\alpha_{3} = {1.0 - \frac{{{RMS}(n)} + 24.0}{- 12.0}}},{\alpha_{4} = {1.0 - \alpha_{3}}}}\end{matrix} & ( {{- 32.0} < {{RMS}(n)} \leq {- 24.0}} ) \\{{\alpha_{1} = {\alpha_{2} = {\alpha_{3} = 0.0}}},{\alpha_{4} = 1.0}} & ( {{{RMS}(n)} \leq {- 32.0}} )\end{matrix}  & (12)\end{matrix}$

In other words, in the case where the root mean square RMS(n) is greaterthan −12 but 0 or less, the distribution ratios are taken to beα₁=1−RMS(n)/−12, α₂=1−α₁, and α₃=α₄−0. Herein, at in the distributionratio α₂ represents the value of the distribution ratio α₁.

Also, in the case where the root mean square RMS(n) is greater than −24but −12 or less, the distribution ratios are taken to be α₁=α₄=0,α₂=1−(RMS(n)+12)/−12, and α₃=1=α₂. Herein, α₂ in the distribution ratioα₃ represents the value of the distribution ratio α₂.

Additionally, in the case where the root mean square RMS(n) is greaterthan −32 but −24 or less, the distribution ratios are taken to beα₁=α₂=0, α₃=1−(RMS(n)+24)/−12, and α₄=1−α₃. Herein, α₃ in thedistribution ratio α₄ represents the value of the distribution ratio α₃.In the case where the root mean square RMS(n) is −32 or less, thedistribution ratios are taken to be α₁=α₂=α₃=0 and α₄=1.

In this way, the weighting controller 102 computes distribution ratiosα₁ to α₄ such that the weights on steeper mapping functions increase asthe root mean square RMS(n) decreases, or in other words, as the volumeof audio based on an input signal decreases overall. In contrast,distribution ratios are computed such that the weights increase onmapping functions with gentler characteristics in segments withhigh-volume audio based on an input signal.

Consequently, amplitude conversion of an input signal is conducted suchthat weights are placed on steeper mapping functions in segments withlow-volume audio in an input signal.

In so doing, once distribution ratios are computed for the mappingfunctions, the multipliers 111-1 to 111-4 multiply output signalssupplied from the mapping processors 101-1 to 101-4 by distributionratios α₁ to α₄, and supply the results to the adder 103.

In the foregoing, it is described that output signals are firstgenerated in the mapping processors 101, and then distribution ratios bywhich to multiply those output signals are computed. However, it mayalso be configured such that mapping processes are conducted aftercomputing distribution ratios.

In such cases, distribution ratios α₁ to α_(M) may be computed on thebasis of mapping control information, for example, and only outputsignals multiplied by non-zero distribution ratios from among thesedistribution ratios are generated by mapping processes. In other words,mapping processes are not conducted on input signals in mappingprocessors 101 which use mapping functions corresponding to adistribution ratio whose value is 0. By configuring it such that onlyoutput signals multiplied by non-zero distribution ratios are generated,the computation load can be further reduced, and a final output signalcan be rapidly obtained.

Also, although distribution ratios are described as being computed byarithmetic computation, it may also be configured such that a table isprepared in which mapping control information values and values ofdistribution ratios α₁ to α_(M) determined by those values are recordedin association with each other, with distribution ratios being acquiredby table lookup.

In step S74, the adder 103 adds together output signals supplied fromthe multipliers 111-1 to 111-M, and generates a single, final outputsignal.

In this way, by using distribution ratios to perform weighted additionof output signals obtained using a plurality of mutually differentmapping functions, amplitude conversion of an input signal using asingle mapping function can be approximately realized. For example, ifthe distribution ratios α₁ and α₂ are taken to be 0 while thedistribution ratios α₃ and α₄ are taken to be given non-zero values,amplitude conversion can be realized using a function havingcharacteristics intermediate between the mapping function f₃(x) and themapping function f₄(x).

By dynamically varying an approximately generated mapping functionaccording to the characteristics in each segment of an input signal,amplitude conversion with a higher degree of freedom can be realizedwith the audio signal processing apparatus 91. In other words, byapproximately generating a mapping function according to per-segmentcharacteristics in each segment of an input signal, amplitude conversioncan be conducted while taking into account not only the characteristicsof a segment, but also the sample value of the sample being processed,similarly to the case of the audio signal processing apparatus 11.

Also, by suitably selecting a mapping function, the dynamic range inaudio volume can be widened, kept the same, or the dynamic range can benarrowed by amplitude conversion.

Once the operation in step S74, the operation in step S75 issubsequently conducted and the conversion process ends. However, sincethe operation in step S75 is similar to the operation in step S13 ofFIG. 2, its description will be omitted.

In so doing, the audio signal processing apparatus 91 conducts mappingprocesses on an input signal by using a plurality of mutually differentmapping functions, performs weighted addition of the obtained pluralityof output signals with distribution ratios obtained from the inputsignal characteristics analysis results, and takes the result as thefinal output signal.

In this way, by selectively using mapping functions according to inputsignal characteristics analysis results to conduct mapping processes andgenerate an output signal, the playback level of an audio signal can beeasily and effectively enhanced without requiring prior analysis orreading ahead of the input signal. Also, faint sounds that have beenconventionally difficult to hear can be made easier to hear, while inaddition, even sounds that have been comparatively loud conventionallybecome even easier to hear.

Meanwhile, the audio signal processing apparatus 91 may likewise beconfigured such that the method for computing mapping controlinformation or distribution ratios is varied according to the outputdevice for the output signal, etc., so as to adjust the degree ofenhancement to the playback level of an audio signal.

Also, although the foregoing describes generating an output signal bycomputing mapping control information and distribution ratios for everysingle sample of an input signal, mapping control information anddistribution ratios may also be computed for every two or moreconsecutive samples.

Fourth Embodiment Configuration of Audio Signal Processing Apparatus

Also, although the case of a one-channel input signal as the audiosignal was described with FIG. 8, an input signal may also be taken tohave plural channels. For example, in the case where a two-channel inputsignal is input, the audio signal processing apparatus may take theconfiguration illustrated in FIG. 11.

The audio signal processing apparatus 141 in FIG. 11 is composed of ananalyzer 21, mapping processors 101-1 to 101-M, a weighting controller102, an adder 103, mapping processors 151-1 to 151-M, a weightingcontroller 152, and adder 153, an output unit 23, and a drive 24. InFIG. 11 herein, like numerals are given to portions corresponding to thecase in FIG. 8, and description of such portions will be reduced oromitted.

Input signals are supplied to the audio signal processing apparatus 141as a left-channel audio signal and a right-channel audio signalconstituting a movie or other content, for example. In other words, theleft-channel input signal is supplied to the analyzer 21 and the mappingprocessors 101-1 to 101-M, while the right-channel input signal issupplied to the analyzer 21 and the mapping processors 151-1 to 151-M.

The analyzer 21 analyzes the respective characteristics of the suppliedleft- and right-channel input signals, generates mapping controlinformation on the basis of the two sets of analysis results thusobtained, and supplies the mapping control information to the weightingcontroller 102 and the weighting controller 152.

The mapping processors 151-1 to 151-M conduct mapping processes on asupplied input signal using the same respective mapping functions usedby the mapping processors 101-1 to 101-M. Also, the mapping processors151-1 to 151-M supply output signals obtained by the mapping processesto the weighting controller 152. Note that hereinafter, the mappingprocessors 151-1 to 151-M will also be simply designated the mappingprocessors 151 in cases where it is not necessary to individuallydistinguish them.

The weighting controller 152 conducts the same operation as theweighting controller 102. In other words, multipliers 161-1 to 161-Mconstituting the weighting controller 152 correspond to the multipliers111-1 to 111-M, multiplying output signals supplied from the mappingprocessors 151-1 to 151-M by distribution ratios α₁ to α_(M) andsupplying the results to the adder 153. Note that hereinafter, themultipliers 161-1 to 161-M will also be simply designated themultipliers 161 in cases where it is not necessary to individuallydistinguish them.

The adder 153 adds together M output signals supplied from themultipliers 161, and supplies the final output signal obtained as aresult to the output unit 23.

[Description of Conversion Process]

Next, a conversion process conducted by the audio signal processingapparatus 141 will be described with reference to the flowchart in FIG.12.

In step S101, the analyzer 21 analyzes the characteristics of suppliedleft- and right-channel input signals. For example, the analyzer 21 mayperform the computation in Eq. 1 discussed earlier, and compute aleft-channel root mean square RMS(n) and a right-channel root meansquare RMS(n).

In step S102, the analyzer 21 generates mapping control information onthe basis of the input signal characteristics analysis results, andsupplies the mapping control information to the weighting controller 102and the weighting controller 152. For example, the analyzer 21 maycompute the average of the left-channel root mean square RMS(n) and theright-channel root mean square RMS(n), and take the obtained average tobe the mapping control information.

Once the operation in step S102 is conducted and mapping controlinformation is generated, the operations in steps S103 to S106 aresubsequently conducted and the conversion process ends. However, sincethese processing operations are similar to the operations in steps S72to S75 of FIG. 9, their description will be reduced or omitted.

However, in steps S103 to S105, mapping processes are conducted in themapping processors 101, the obtained output signals are multiplied bydistribution ratios in the multipliers 111, the output signals whichhave been multiplied by the distribution ratios are added together inthe adder 103, and the result is taken to be the final left-channeloutput signal. Similarly, mapping processes are conducted in the mappingprocessors 151, the obtained output signals are multiplied bydistribution ratios in the multipliers 161, the output signals whichhave been multiplied by the distribution ratios are added together inthe adder 153, and the result is taken to be the final right-channeloutput signal.

In so doing, the audio signal processing apparatus 141 analyzes thecharacteristics of left- and right-channel input signals, generatescommon mapping control information for the left and right channels, anduses the obtained mapping control information to compute a commondistribution ratio for the left and right channels for each mappingfunction. By using common mapping control information for the left andright channels to compute common distribution ratios for the left andright channels for each mapping function in this way, the playback levelof an audio signal can be enhanced without changing the inter-channelvolume balance.

The series of processes discussed in the foregoing may be executed inhardware, but may also be executed in software. In the case of executingthe series of processes in software, a program constituting suchsoftware is installed from a program recording medium to a computerbuilt into special-purpose hardware, or a computer such as ageneral-purpose personal computer, for example, able to execute variousfunctions by installing various programs thereon.

FIG. 13 is a block diagram illustrating an exemplary hardwareconfiguration of a computer that executes the series of processesdiscussed in the foregoing with a program.

In a computer, a CPU (Central Processing Unit) 201, ROM (Read-OnlyMemory) 202, and RAM (Random Access Memory) 203 are connected to eachother by a bus 204.

An input/output interface 205 is additionally connected to the bus 204.Connected to the input/output interface 205 are an input unit 206comprising a keyboard, mouse, microphone, etc., an output unit 207comprising a display, speakers, etc., a recording unit 208 comprising ahard disk, non-volatile memory, etc., a communication unit 209comprising a network interface, etc., and a drive 210 that drives aremovable medium 211 such as a magnetic disk, an optical disc, amagneto-optical disc, or semiconductor memory.

In a computer configured as above, the series of process discussed inthe foregoing is conducted due to the CPU 201 loading a program recordedin the recording unit 208 into the RAM 203 via the input/outputinterface 205 and the bus 204, and executing the program, for example.

A program executed by the computer (CPU 201) may for example be providedby being recorded onto a removable medium 211 as an instance of packagedmedia consisting of magnetic disks (including flexible disks), opticaldiscs (including CD-ROMs (Compact Disc-Read-Only Memory), DVDs (DigitalVersatile Disc), etc.), magneto-optical discs, or semiconductor memory.Alternatively, a program may be provided via a wired or wirelesstransmission medium such as a local area network, the Internet, ordigital satellite broadcasting.

Additionally, a program may be installed to the recording unit 208 viathe input/output interface 205 by loading the removable medium 211 intothe drive 210. Also, a program may be received by the communication unit209 via a wired or wireless transmission medium and installed to therecording unit 208. Otherwise, a program may be installed in advance tothe ROM 202 or the recording unit 208.

Herein, a program executed by a computer may be a program in whichoperations are conducted in a time series following the order describedin this specification, but may also be a program in which operations areexecuted in parallel or at required timings, such as upon being called.

Furthermore, an embodiment of the present invention is not limited tothe embodiments discussed in the foregoing, and various modificationsare possible within a scope that does not depart from the principalmatter of the present invention.

REFERENCE SIGNS LIST

-   -   11 audio signal processing apparatus    -   21 analyzer    -   22 mapping processor    -   61 mapping processor    -   101-1 to 101-M, 101 mapping processors    -   102 weighting controller    -   103 adder    -   151-1 to 151-M, 151 mapping processors    -   152 weighting controller    -   153 adder

The invention claimed is:
 1. A signal processing apparatus comprising: acircuitry configured to initiate an analysis of input signalcharacteristics; initiate an amplitude conversion of the input signal onthe basis of a predetermined linear function or nonlinear function;initiate a multiplication of a plurality of the input signals, whichhave been respectively amplitude-converted on the basis of a pluralityof mutually different functions, by respective weights determined by aresult of the analysis of the input signal characteristics; and initiatea generation of an output signal by adding together the plurality of theinput signals which have been multiplied by the weights, wherein as avolume of audio based on the input signal decreases overall, theamplitude conversion of the input signal is conducted using a mappingfunction having a steeper slope.
 2. The signal processing apparatusaccording to claim 1, wherein the circuitry is further configured toinitiate a computation of a value expressing an average sample value ofsamples included in a given segment of the input signal as the analysisresult.
 3. The signal processing apparatus according to claim 2, whereinthe analysis result is a root mean square or a moving average of samplevalues of samples included in the given segment.
 4. The signalprocessing apparatus according to claim 1, wherein in a case whereamplitude conversion is conducted on the input signal for each of aplurality of channels to generate an output signal for each channel, oneanalysis result is computed and shared by all channels.
 5. The signalprocessing apparatus according to claim 1, wherein the weights aredetermined by the analysis result for every single sample of the inputsignal.
 6. The signal processing apparatus according to claim 1, whereinthe weights are determined by the analysis result for every given numberof two or more consecutive samples of the input signal.
 7. A signalprocessing method comprising: analyzing input signal characteristics,conducting amplitude conversion of the input signal on the basis of apredetermined linear function or nonlinear function, respectivelymultiplying a plurality of the input signals, which have beenamplitude-converted on the basis of a plurality of mutually differentfunctions, by weights determined by a result of the analysis of theinput signal characteristics, and generating an output signal by addingtogether the plurality of input signals which have been multiplied bythe weights, wherein as a volume of audio based on the input signaldecreases overall, the amplitude conversion of the input signal isconducted using a mapping function having a steeper slope.
 8. A signalprocessing apparatus comprising: a circuitry configured to initiate ananalysis of input signal characteristics; and initiate a generation ofan output audio signal by conducting amplitude conversion of the inputsignal on the basis of a nonlinear function determined by a result ofthe analysis of the input signal characteristics, wherein as a volume ofaudio based on the input signal decreases overall, the amplitudeconversion of the input signal is conducted using a mapping functionhaving a steeper slope.
 9. The signal processing apparatus according toclaim 8, wherein the circuitry is further configured to initiate acomputation of a value expressing an average sample value of samplesincluded in a given segment of the input signal as the analysis result.10. The signal processing apparatus according to claim 9, wherein theanalysis result is a root mean square or a moving average of samplevalues of samples included in the given segment.
 11. The signalprocessing apparatus according to claim 8, wherein in a case whereamplitude conversion is conducted on the input signal for each of aplurality of channels to generate an output signal for each channel, oneanalysis result is computed and shared by all channels on the basis ofthe input signals in the plurality of channels.
 12. The signalprocessing apparatus according to claim 8, wherein the nonlinearfunction is determined by the analysis result for every single sample ofthe input signal.
 13. The signal processing apparatus according to claim8, wherein the nonlinear function is determined by the analysis resultfor every given number of two or more consecutive samples of the inputsignal.
 14. A signal processing method comprising: analyzing inputsignal characteristics, and generating an output audio signal byconducting amplitude conversion of the input signal on the basis of anonlinear function determined by a result of the analysis of the inputsignal characteristics, wherein as a volume of audio based on the inputsignal decreases overall, the amplitude conversion of the input signalis conducted using a mapping function having a steeper slope.